This invention relates to a fluid flow control apparatus and method. More particularly, this invention relates to apparatus and method for controlling the rate of fluid flow from a source of pressurized fluid such as a compressor of a turbine engine to an enclosure such as an aircraft cabin.
Modern aircraft having a turbine engine such as a turboprop or turbofan engine conventionally utilize air bled from the compressor of the engine to pressurize the aircraft cabin and to provide a ventilating flow of fresh air through the cabin. The ventilating flow requirements of the aircraft cabin vary directly with the number of passengers therein. Consequently, the cabin pressurizing and ventilating system must provide for a bleed air flow corresponding to the maximum number of passengers which the cabin will accommodate. However, bleeding air from the compressor of a turbine engine has a detrimental effect upon the fuel efficiency of the engine. Consequently, when the cabin is not fully occupied, a reduction in the rate of ventilating airflow is desirable in order to preserve engine fuel efficiency.
To this end, conventional aircraft pressurizing and ventilating systems have provided for step-wise variation of the ventilating flow rate. Thus, a ventilating air flow rate approximating the percentage of cabin occupancy may be arrived at by operating the system on one of the steps between zero and 100 percent flow rate. For example, one oonventional system provides steps of zero, 68 percent, and 100 percent flow rate. Obviously, such a step-wise variation of air flow rate allows only a very rough approximation of the cabin occupancy percentage, particularly when only a few steps are provided. Thus, an excessive ventilating air flow rate is usually provided at the expense of decreased engine fuel efficiency.
In view of the recognized deficiencies of conventional aircraft cabin pressurizing and ventilating systems, it is an object for this invention to provide an apparatus and method for controlling the rate of air flow to an aircraft cabin which allows infinite or step-less variation of the air flow rate over a selected part of the operating range of the apparatus.
Another object for this invention is to provide a fluid flow control apparatus and method wherein a pair of fluid flow sensors having differing sensing characterisitics are exposed to fluid flowing in a duct to produce a pair of signals analogous to the fluid flow and differing from one another; and blending the pair of signals to produce a third signal controlling the fluid flow rate.
Yet another object is to provide a fluid flow control apparatus and method wherein a pair of signals are supplied to a valve device blending the pair of signals to produce a third signal according to an operator input to an actuator of the valve device.
In summary, this invention provides a fluid flow control apparatus and method wherein a duct communicates pressurized air form a source thereof to an enclosure. A pair of fluid flow sensors having differing sensing characteristics are exposed to fluid flowing in the duct to produce a pair of signals analogous to the fluid flow rate in the duct and differing from one another. The pair of signals are blended according to an operator input to produce a third signal. A valve device is disposed in the duct to open and close communication therethrough in response to the third signal so that the fluid flow rate into the enclosure is scheduled according to the operator input.
Further objects and advantages of the invention will be apparent in light of the following detailed description of a preferred embodiment of the invention.